The epitaxial silicon wafer has been widely used for many years as a wafer for producing an individual semiconductor, a bipolar IC, or the like because of the outstanding characteristics thereof. Moreover, since a soft error and a latch-up quality thereof are excellent also as for MOS LSI, it has been widely used for a microprocessor unit or a flash memory device. Furthermore, the need of epi-wafer has been expanded increasingly in order to reduce lowering of reliability of DRAM due to a so-called grown-in defect introduced at the time of production of a silicon single crystal.
If a heavy metal impurity exists in the epi-wafer used for such a semiconductor device, it will become a cause of poor characteristics of the semiconductor device. Cleanliness needed especially for the latest device is considered to be a concentration of a heavy metal impurity of 1×109 atoms/cm2 or less, and thus the heavy metal impurity existing in epi-wafer should be decreased as much as possible.
There is a gettering technique as one of the techniques for reducing such a heavy metal impurity, and the importance of the gettering technique is becoming higher in recent years. One of the very effective methods as gettering technique is a method called Intrinsic gettering (IG) wherein oxygen precipitates (BMD: Bulk micro defect) are formed in a silicon wafer, and a heavy metal impurity is caught at the distorted place. However, since the epi-wafer is generally subjected to high temperature heat treatment in order to deposit an epitaxial layer (hereinafter occasionally referred to as just “epi-layer”) on a silicon wafer, the nuclei of oxygen precipitation which have been grown to some extent in the heat environment at the time of growing of crystal are disappeared due to the high temperature heat treatment in the epitaxial process, and it may cause a problem that BMD is hard to be formed.
Then, in order to solve such a problem, it has been proposed in Japanese Patent Application Laid-open (Kokai) No. 2000-44389, that the silicon single crystal in which nitrogen is doped is used as a substrate on which an epitaxial layer is formed. If nitrogen is doped, the nucleus of oxygen precipitation due to nitrogen (uneven nucleus) is formed in the silicon single crystal, and the nucleus of oxygen precipitation cannot be disappeared easily in heat treatment at the time of formation of the epi-layer, and thus the epi-wafer with high gettering capability can be produced.
On the other hand, it has been known that stacking faults (SF) will be generated on an epi-layer in an epi-wafer. If a device is produced on SF generated in the epi-layer, leak of electric current or the like will be generated and it will cause poor characteristics. It is known that if impurity exists on a substrate, the SF is formed with it as a starting point in the process wherein an epi-layer is being deposited. Therefore, in the case that an epi-layer is formed, the epi-layer is usually formed with being controlled so that impurities such as a particle may not exist on a substrate.
However, it was made clear that the cause of generation of SF in an epi-layer is generated due to not only impurities such as a particle, but also grown-in defects which exist near the surface of the wafer formed at the time of growth of the silicon single crystal as a starting point, as indicated in Japanese Patent. Application Laid-open (Kokai) No. 2001-151596. It was also revealed that the probability is very high in the epi-wafer in which nitrogen is doped as compared with the epi-wafer in which nitrogen is not doped. In Japanese Patent Application Laid-open (Kokai) No. 2001-151596, it is proposed to use as a substrate the wafer in which a grown-in defect does not exist in a surface layer in order to prevent generation of SF. Specifically, it is proposed to use as a substrate for epitaxial growth the wafer sliced from a single crystal produced so that grown-in defects may not be generated using the special manufacture condition wherein a rate of crystal growth is strictly controlled when the crystal is grown, or the wafer subjected to annealing processing to eliminate defects in a surface layer of the wafer.
However, such methods may cause significant lowering of productivity and a remarkable cost rise in production of an epitaxial wafer, since they use a special method for producing a crystal, and the wafer wherein no crystal defect exists in a surface layer of the wafer should be produced by performing annealing processing which needs special equipment and operation cost, according to these methods.